In the technical field for insulating materials that are used for semiconductors, multilayer printed substrates, and the like, along with the thickness reduction of various electronic members, or with speed improvement and frequency increase of signals, there is a demand for the development of new resin materials in accordance with these market trends. For example, as a result of thickness reduction of electronic members, heat-induced “warpage” of those members becomes noticeable, and in order to suppress this, development of resin materials having low cure shrinkage and high dimensional stability is in progress. Furthermore, in regard to the speed improvement and frequency increase of signals, in order to reduce energy loss caused by heat generation or the like, development of resin materials that produce cured products having low values for both the dielectric constant and the dielectric loss tangent is in progress.
In a known technology, a resin material capable of forming a cured product having a relatively low dielectric constant and a relatively low dielectric loss tangent, such as an active ester resin obtained by esterifying a dicyclopentadiene phenol resin and α-naphthol with phthalic acid chloride, is used as a curing agent for epoxy resins (see PTL 1 described below). The active ester resin described in PTL 1 is characterized by being capable of forming a cured product having a low dielectric constant and a low dielectric loss tangent as compared with the case of using a curing agent of a conventional type such as a phenol novolac resin. However, the active ester resin does not meet the level of market requirements in recent years, and particularly, there is a demand for a further reduction in the value of the dielectric loss tangent. Furthermore, there is a demand for a further reduction in the cure shrinkage.